1. Field of the Invention
The present invention relates to an exhaust gas purging catalyst and a method for producing the exhaust gas purging catalyst. More in detail, the above exhaust gas purging catalyst includes a catalyst coat layer having a special layer structure.
2. Description of the Related Art
An exhaust gas and the like of an automobile has an extremely high gas flow rate. Therefore, an exhaust gas purging catalyst has to purge the exhaust gas in a short-time contact with the exhaust gas. Is this case, however, the exhaust gas is unlikely to be diffused into an inner part of a catalyst coat layer of the exhaust gas purging catalyst.
In this connection, EP1364706 (family of JP2002253968 [=Japanese Patent Application Laid-Open No. 2002-253968] and WO02070127) and JP2004025013 (=Japanese Patent Application Laid-Open No. 2004-025013) each propose controlling of the pore diameter and pore capacity of the catalyst coat layer, so as to improve exhaust gas diffusing property.
On the other hand, conventionally, the exhaust gas purging catalyst is required to show a high purging performance even when the air-to-fuel ratio is fluctuated. For example, in an oxidation atmosphere (lean atmosphere), a promoter (co-catalyst) having an Oxygen Storage Capacity (though acronymed by OSC, this functionally means oxygen storing and discharging capacity) is disposed adjacent to a noble metal, so as to secure the purging performance.